#!/bin/sh

[ $# -eq 1 ] || {
	echo 1>&2 "usage: socat TCP-LISTEN:44322,fork EXEC:'$0 <DBFILE>'"
	exit -1
}

DBFILE="$1"
touch $DBFILE

numlines() { wc -l <"$DBFILE"; }

while read line; do
	case "$line" in
	(SEND\ *)
		echo "${line##SEND\ }" >>"$DBFILE"
		echo $(numlines) ;;
	(SKIP\ *)
		num="${line##SKIP\ }"
		len=$(numlines)
		slen=$((len - num))
		slen=$((slen < 0 ? 0 : slen))
		echo "$slen"
		head -n "$len" <"$DBFILE" | tail -n "$slen"
		echo "$len" ;;
	(LAST\ *)
		num="${line##LAST\ }"
		len=$(numlines)
		slen=$((len > num ? num : len))
		echo "$slen"
		head -n "$len" <"$DBFILE" | tail -n "$slen"
		echo "$len" ;;
	(POLL\ *)
		len=$(($(numlines) - ${line##POLL\ }))
		echo $((len < 0 ? 0 : len)) ;;
	(HIST)
		len=$(numlines)
		echo "$len"
		head -n "$len" <"$DBFILE"
		echo "$len" ;;
	(QUIT)
		exit 0 ;;
	esac
done